libexport.a: Replace matchhostname()

So that exportfs can eventually support IPv6 addresses, copy statd's
getaddrinfo(3)-based matchhostname to exportfs, with adjustments for
dealing with export wildcards and netgroups.  Until exportfs has full
IPv6 support, however, we want to ensure that IPv6 addresses continue
to remain blocked in the address comparison code used by exportfs.  At
a later point we'll replace much of this with the generic functions
in sockaddr.h.

Since it contains special logic for handling wildcard and netgroups,
this function is specialized for exportfs, and does not belong in
one of the shared libraries.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>